Question

所以我已经完成了关于SO的几乎所有问题，并且我已将它们全部放在一起创建一个接受两个参数的方法，首先是要在{{1中下载和显示的图像的URL第二个是UIImageView的占位符图像。我想保存图像，以便每次都不会下载。我使用SDWebImage下载图像，但是当使用SDWebImage将图像保存在文档目录中时我有些困惑，所以我决定不使用它。我使用UIImageView，我的方法现在看起来像：

dispatch_sync(dispatch_get_main_queue()

我有几个问题，这个实现是否足够好，因为我正在开发应用程序商店的应用程序？从URL下载图像是否会异步完成？（我知道我正在使用- (void)saveImageFromURL:(UIImage*)image:(NSURL*)imageURL { NSString *url = [imageURL absoluteString]; NSArray *parts = [url componentsSeparatedByString:@"/"]; NSString *filename = [parts lastObject]; NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png", filename]]; BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:fullPath]; if (fileExists) { NSLog(@"File already exists"); _myUIImage.image = [UIImage imageNamed:fullPath]; return; } else { dispatch_async(dispatch_get_main_queue(), ^{ [self.myUIImage sd_setImageWithURL:imageURL placeholderImage:image]; UIImage *imageFromURL = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageURL]]; NSData *imageDataNew = UIImagePNGRepresentation(imageFromURL); NSFileManager *fileManager = [NSFileManager defaultManager]; [fileManager createFileAtPath:fullPath contents:imageDataNew attributes:nil]; }); } }，但只需要确认）。如果是，那么这不会阻止我的用户界面，对吗？

Answer 1

dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){

// *** Load Image from URL Asynchronously without blocking Main thread ***    
UIImage *imageFromURL = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageURL]];

    dispatch_async(dispatch_get_main_queue(), ^(void){

        // *** Create file path to DocumentDirectory ***
        NSString * docDirPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
        NSString *filePath = [docDirPath stringByAppendingPathComponent:@"myImage.jpg"]

        // *** Write Image to disk *** 
        BOOL isSaved = [UIImageJPEGRepresentation(image, 1.0f) writeToFile:dirPath atomically:YES];
        if(isSaved)
        {
            NSLog(@"Image write to disc successfully.");
        }
    });
});

异步保存URL中的图像

1 个答案: